1. Field of the Invention
The invention relates in general to a power supply system of a light source and light source actuating method, and more particularly to a power supply system of a light source and light source driving method, which can prevent light sources from overloading.
2. Description of the Related Art
Along with the coming digital era and wide spread of the computer network, the display has an inevitable tendency to be flat and thin in design. The power supply system of a light source is an essential component for driving the light source in the flat display. It determines the reliability and stability of the light source and directly affects the image quality of the flat display.
Referring to FIG. 1, a block diagram of a power supply system of a conventional light source is shown. The power supply system 100 of a light source includes a voltage transformer 110, a feedback circuit 120 and a control circuit 130. The voltage transformer 110 receives a direct current (DC) input voltage DC and transforms the DC input voltage DC into an alternating current (AC) voltage AC for the light source 10 according to a power control signal C1. The feedback circuit 120 is used for receiving the feedback current I1 outputted by the light source 10 and generating a feedback voltage L1 for the control circuit 130 according to the feedback current I1. The control circuit 130 receives a turn-on signal SON, luminance adjusting signal VAdjust and feedback voltage L1 and accordingly generates a power control signal C1.
The AC voltage AC received by the light source 10 includes an actuation voltage and an operational voltage. The actuation voltage has a higher voltage level than the operational voltage, and the levels of the actuation voltage and operational voltage are both affected by the frequency and duty cycle of the power control signal C1 outputted by the control circuit 130. The actuation voltage should have an enough high level to reach a breakdown voltage of the light source 10 such that the light source 10 can be lighted up. After the light source 10 is lighted up, the AC voltage AC is adjusted to be the operational voltage.
As shown in FIG. 3A, before the time point t1, the light signal SON is not inputted to the power supply system 100 and thus the light source 10 is not actuated. At the time, the luminance adjusting signal Sba can maintain at any voltage level set by the user. At the time t1, the turn-on signal SON is inputted to the power supply system 100 for actuating the light source 10 and the luminance adjusting signal Sba still maintains the voltage level set by the user.
However, in the process of transforming the voltage AC to be the operational voltage, if unsuitably controlled, between the time points t1 and t2 when the turn-on signal SON and the luminance adjusting signal Sba function at the same time, the duty cycle of the power supply system 100 of the light source will exceed limitation, and consequently, the power supply system 100 stops operating.
Therefore, how to prevent the power supply system exceeds the limitation of the duty cycle in the process of lighting the light source is an essential issue to be resolved.